EM radiation generated by fields of an electron beam passing by a periodic structure was first observed by Smith and Purcell in 1953. At that time, they grazed an electron beam over a metallic diffraction grating with a 1.67 μm spacing and observed visible light in the 450-550 nm range. Since this demonstration, a number of different techniques have used the Smith-Purcell effect to produce infrared (IR) sources, microwave sources, and particle beam diagnostics.
However, a more intense source of EM radiation ranging from the EUV range up to the hard X-ray range may be beneficial.